1. Field of the Invention
The present invention relates to a peak-torque descending composition for lowering a peak torque at a slide initiation of a precision machine or component having a sliding portion, particularly, a peak-torque descending composition effective for lowering the peak torque at an initiation of a watch component, a part having a sliding portion using the composition, a process for producing a precision machine or component having a sliding portion using the peak-torque descending composition, and a precision machine or component produced by the process.
Further, the present invention relates to a press fit method capable of preventing a deformation (referred to as so-called xe2x80x9ca burr of metalxe2x80x9d) that peripheral portions of a hole on a metal plate are lifted up when a metal shaft is pressed into the metal plate.
2. Description of the Related Art
Precision machines and components having a sliding portion are mostly made of metals and plastics. Considerable numbers of metallic components are made by imbedding two or more tiny parts. The reasons why they are made by imbedding are that there are cases of letting the parts slide into one another in addition to the case that the parts cannot be integrally processed in a process for the production. When metals are pressed into one another by pressure, adhesion and fusion bond generally occur. A peak torque is produced when tried to slide a portion of adhesion or fusion-bond. In the cases of precision machines made of a combination of metallic and plastic components, there are some cases where the peak torque at the initiation of slide must be lowered to an appropriate and stable level of the peak torque which does not damage the plastic component, because the plastic component is potentially damaged when the peak torque is too large.
The most common watch as a precision machine is described below. The present invention is not limited to watch mechanism, but can be used for, for example, components for bearing and the like.
Watches are broadly divided into mechanical and electronic watches. The mechanical watches are operated by spiral spring as driving source, whereas the electric watches are operated by electric power. In both of the mechanical and electronic watches, a time is displayed by combining a gear train wheel portion assembling rotating gearwheels to drive an hour hand, a minute hand and a second hand and a sliding portion such as a lever. Metals and plastics are used as materials for watches considering processability and strength.
The watch has a function to adjust a time. In order to adjust the time, a slip mechanism is required to rotate an hour hand and a minute hand with fixing a second hand at a constant location (e.g., a location of 12 o""clock) both in the mechanical and electric watches.
In a transmission system of the watch, a magnetic rotor is rotated at 180 degrees per second. This is transmitted in the following sequence to drive each hand. In the transmission system, a motion is transmitted sequentially from the rotor, a fifth wheel, a fourth wheel (drive a second hand), a third wheel, a center wheel (drive a minute hand), a minute wheel and a hour wheel (drive a hour hand).
Generally in the watch, when a crown is pulled to adjust the time, a clutch wheel is connected to the minute wheel, and in this state when the crown is rotated, the clutch wheel is rotated. When the clutch wheel is rotated, the hour wheel is rotated through the minute wheel to be able to move the hour hand. Also, the minute wheel rotates a center wheel pinion. Since the minute hand is attached to the center wheel pinion, the minute hand can be rotated. That is, by rotating the minute wheel, the time can be adjusted with engaging the hour and minute hands simultaneously by rotating the crown.
Since the train wheel portion of the watch is engaged, the rotor will be also rotated if leaving as it is. Therefore, the slip mechanism to rotate only necessary gearwheels is provided not to rotate the rotor by combining with a brake mechanism.
The watch is generally provided with a portion to perform slip in the center wheel.
The slip mechanism essentially functions to adjust the time, and an appropriate torque and no large value of the peak torque at an initial rotation are desired. When the peak torque is high, if a less rigid plastic material and the like are used as parts from the rotor to the third wheel, the gearwheels made of such a material are chipped to damage the watch.
There have been various proposals as structures of the center wheel which is a gearwheel body having the slip mechanism.
For example, Japanese Patent No. 2808842 describes a process for producing a watch component by incorporating a watch gearwheel into a base component when assembling a watch comprising the watch gearwheel having a slip portion between a gearwheel shaft and a gearwheel portion and the base component supporting the watch gearwheel on a shaft, by employing a method of lubrication on the surface portion opposite to the gearwheel portion and proximate to the slip portion in the base component. In this process, lubrication is carried out before incorporating the watch gearwheel into the base component, and it is not carried out in other steps, and thus, if the condition of no lubrication before the incorporation occurs, there is a possibility that the resultant watch component becomes an inferior article. Additionally, this method has a problem in that handling of stickiness with oil and so on becomes complicated since oil adheres to the components.
Japanese Patent No. 2795809 proposes a slip mechanism applied for a minute hand wheel and so on of the watch, which is a structure of a part supporting the slip portion. According to the slip mechanism of the watch described in this patent, the watch components having a slip mechanism can be assembled with a slight force. However, phenomena of adhesion and fusion bond of metals one to another arise after the components are assembled because the metals are grazed one to another at the assembling, and the peak torque becomes high when slipped in the initial stage. Thus, this mechanism has a problem in that the gearwheels are chipped in a watch using plastic gearwheels.
Japanese Patent Publication No. 16705/1996, Japanese Patent Laid-Open Nos. 123783/1994 and 196747/1993 propose a center wheel (also referred to as a second wheel) combining a metal pinion and a resin gearwheel. In the slip mechanism of the watch described in these patents, there are problems that the production of watch components takes much time and requires complicated procedures due to the complex structure, and abrasion resistance is inferior since the slip portion is resin.
Accordingly, the present inventors have made intensive studies to solve the above problems, and as a result, they have found that by a process comprising the steps of immersing a metal gearwheel or a metal pinion in a composition containing from 0.01 to 5% by weight of an extreme pressure agent (anti-seizing agent) comprising a neutral phosphate ester and/or neutral phosphite ester in a solvent of a hydrocarbon and/or ether to adhere or absorb the composition to the surface thereof, immediately thereafter, taking out the gearwheel or the pinion from the composition, and drying, prior to assembling the gearwheel body having a slip mechanism of the metal gearwheel and the metal pinion, a gearwheel body can be assembled without developing a large peak torque at an initial stage when slipped and chipping wheel teeth of the gearwheel even when the plastic gearwheel is used. Also, they have found that a burr phenomenon does not occur on a metal plate when a metal shaft without such surface treatment is press-fitted into a hole of a metal plate of which surface is treated as in the above manner using the composition. Further, they have found that a burr phenomenon does not occur on a metal plate when a metal shaft of which surface is treated as in the above manner using the composition is press-fitted into a hole of a metal plate without such surface treatment. Based on these findings, the present invention has been completed.
The present invention is made to solve the problems of the prior art as described above, and an object of the invention is to provide a peak-torque descending composition capable of assembling a gearwheel body having a slip mechanism which can be made from metallic materials with a simple structure wherein a large peak torque is not produced in an initial stage when slipped and wheel teeth of the gearwheel are not chipped even when the gearwheel is plastic, a part having a sliding portion such as a gearwheel portion and the like using the composition, a process for producing a component or precision machine having a sliding portion using the above composition, and a component or precision machine produced by the process.
Another object of the present invention is to provide a press fit method for preventing the occurrence of a burr phenomenon on pressing a shaft into a metal plate.
The peak-torque descending composition of the present invention contains 0.01 to 5% by weight of an extreme pressure agent comprising at least one member selected from the group consisting of neutral phosphate esters and neutral phosphite esters in a solvent comprising at least one member selected from the group consisting of hydrocarbons and ethers.
The peak-torque descending composition of the present invention may further contain at least one corrosion inhibitor (antirust agent) selected from the group consisting of ester corrosion inhibitors, corrosion inhibitors of partial esters of isodecyl succinate and ethylene oxide (ASA) and straight-chain fatty acid corrosion inhibitors.
For the peak-torque descending composition for drying at normal temperatures, the boiling point of the solvent is preferably 130xc2x0 C. or below.
The concentration of the corrosion inhibitor is preferably from 0.01 to 0.5% by weight based on 100% by weight of the peak-torque descending composition and is preferably equal to or less than the concentration of the extreme pressure agent.
The part having a sliding portion of the present invention is characterized in that the surface is treated with the peak-torque descending composition of the present invention.
As the part having a sliding portion, watch parts can be mentioned.
The above part of the present invention includes, for example, a gearwheel body having a slip mechanism and having a metal gearwheel and a metal pinion, wherein at least one of the gearwheel and the pinion is surface-treated with the peak-torque descending composition of the present invention prior to assembling the gearwheel body (e g., watch parts) using the gearwheel and pinion.
The process for producing a component or precision machine having a sliding portion of the present invention comprises immersing a part having a sliding portion in the peak-torque descending composition of the present invention, adhering or absorbing the composition onto the surface of the part, immediately thereafter, taking out the part from the composition, followed by drying, and assembling a component or precision machine using the parts.
The component or precision machine having a sliding portion of the present invention is a component or precision machine produced by the above process.
Specific examples of the assembled component include a gearwheel body for a watch having a slip mechanism and comprising a metal gearwheel and a metal pinion. Also, specific examples of the precision machines include a watch using the gearwheel body.
In the process for producing a component or precision machine of the present invention, the drying is preferably a drying at normal temperatures, and especially warm air drying at normal temperatures is preferable.
The press fit method of the present invention comprises, prior to pressing a metal shaft into a metal plate, immersing the metal plate or the shaft in the peak-torque descending composition of the present invention and adhering or absorbing the composition onto the inner surface of a hole for press fit of the metal plate or the surface of the shaft, immediately thereafter, taking out the metal plate or the shaft from the composition, and drying.